Afaics, non-deceptively mined proof-of-work issued tokens entirely avoid MLM scam and securities laws and thus are legal. Many major nation-states have declared that Bitcoin is legal. Some nations have declared Bitcoin is currency, others such as IRS in USA declared it is property, and for example FInCEN in the USA has stated that for example Bitcoin mining is legal.

As for ICO issued tokens, please read this further explanation.

Example exchanges: if it is illegal to exchange decentral exchanges must and will evolve.

I’m going to analyse this aspect more in my next blog.

The mainstream of society has no compelling reason to incriminate themselves unless it's to join a speculative bubble. Afaik, the liquidity of truly decentralized exchanges has been pitiful thus far. Afair, for example Bitsquare is not truly decentralized and the escrow agents are the enforcement Achilles heel.